Book/Report

FZJ-2019-01665

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Atomare Mechanismen der Legierungsbildung an Oberflächen : eine Untersuchung mit dem Rastertunnelmikroskop am Beispiel des Systems Mn/Cu (100)

Flores-Pyttel, T. (Corresponding author)FZJ*

1996
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/21739

Report No.: Juel-3295

Abstract: Atomic processes important in surface alloy formation for MnlCu(100) have been studied using STM (Scanning Iunneling Microscopy). The investigations were performed for coverages between 0.005 and 1.0 monolayers (ML) deposited around and above 300 K. Due to a pronounced corrugation incorporated Mn atoms are imaged as small protrusions allowing the distinction between Mn and Cu atoms in the STM images. The height of the protrusions was determined to approximately 0.3 $\mathring{A}$. Mn is incorporated in the Cu(100) surface layer already at very low coverages ($\approx$ 0.005 ML Mn). No critical coverage for the incorporation of Mn was found. Below 0.25 ML Mn the incorporated Mn atoms are disordered. Around and above 0.25 ML Mn an ordering process into a c(2x2) structure starts which is completed at 0.5 ML Mn. The STM images of the c(2x2) surface alloy only show one type of atom. With regard to the strong corrugation of incorporated Mn at lower coverages presumably the Mn atoms are imaged. For small coverages a diffusion coefficient of D = 5,3 $\cdot$10$^{-18}$ cm$^{2}$s$^{-1}$ is determined from anevaluation of the Einstein relation. Different models for the diffusion of incorporated Mn are discussed. The experimental observations can be explained successfully by a diffusion mechanism that is based on diffusing surface vacancies. Lower and upper limits for the jump frequency of incorporated Mn atoms are derived from the STM images for several coverage regimes. This analysis shows that the mobility of incorporated Mn around 0.3 ML Mn is between one and two orders of magnitude higher than at low coverages. On the surface a ripening of alloyed islands is observed. Large islands grow at the expense of small islands. The mass transport between the islands is mediated by a particle transfer. Such a late-stage growth is called Ostwald-ripening. The ripening is particularly pronounced in the coverage regime where the mobility of the incorporated Mn is enhanced. This indicates that vacancies also playa decisive role for Ostwald-ripening in this system. The Mn atoms are preferentially incorporated in the vicinity of island edges and substrate steps. In the proximity of substrate steps, the rate of incorporation into the lower terrace increases with the kink density of the steps. This implies that the incorporation in the lower terrace is particularly effective near kinks. Different models responsible for the incorporation in the lower terrace are suggested. The experimental observations can be understood by kink-induced atomic exchange processes or by recombination processes between atoms and vacancies. The alloying of the upper terrace of substrate steps is driven by an attachment of Mn adatoms. This process is essentially independent of the step orientation. Therefore, the concentration of incorporated Mn in the vicinity of steps does not depend upon the step direction. Step fluctuations and vacancy mediated diffusion enable a transport of the attached Mn atoms into the upper terrace. The diffusion of the incorporated Mn atoms leads to a more homogeneous Mn distribution in the course of the time.

---

Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

---

Database coverage:

---